1. Field of the Invention
The present invention relates generally to a multi-hop relay Broadband Wireless Access (BWA) communication system and, in particular, to a scanning apparatus and method in a multi-hop relay BWA communication system.
2. Description of the Related Art
Provisioning of services with diverse Quality of Service (QoS) levels at about 100 Mbps to users is an active study area for a future-generation communication system called a 4th Generation (4G) communication system. Particularly, active research is conducted on provisioning of high-speed service by ensuring mobility and QoS to a BWA communication system such as Wireless Local Area Network (WLAN) and Wireless Metropolitan Area Network (WMAN). Such major examples are Institute of Electrical and Electronics Engineers (IEEE) 802.16a and IEEE 802.16e.
The IEEE 802.16a and IEEE 802.16e communication systems are implemented by applying Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to physical channels of the WMAN system. IEEE 802.16a considers only a single-cell structure with no regard to mobility of a Subscriber Station (SS). In contrast, IEEE 802.16e supports SS mobility in the IEEE 802.16a communication system. A Mobile Subscriber Station is called an MSS.
FIG. 1 shows a typical IEEE 802.16e communication system configured in a multi-cell structure. The system includes cells 100 and 150, Base Stations (BSs) 110 and 140 for managing the cells 100 and 150, respectively, and a plurality of MSSs 111, 113, 130, 151 and 153. Signals are sent and received between the BSs 110 and 140 and the MSSs 111, 113, 130, 151 and 153 in OFDM/OFDMA. The MSS 130 exists in a cell boundary area between the cells 100 and 150, i.e. in a handover region. When the MSS 130 moves to the cell 150 managed by the BS 140 during signal transmission/reception to/from the BS 110, the serving BS of the MSS 130 changes from the BS 110 to the BS 140.
FIG. 2 shows signal flow between an MSS and a BS, for scanning in a conventional BWA communication system. An MSS 210 communicates with a serving BS 230 in step 211. During the communication, the MSS 210 determines whether to scan pilot channel signals from the serving BS 230 and neighbor BSs. If scanning should be performed, the MSS 210 sends a Mobile Scanning Interval Allocation Request (MOB_SCN-REQ) message to the serving BS 230 in step 213. The MOB_SCN-REQ message has the following configuration illustrated in Table 1 below.
TABLE 1SyntaxSize (bits)NotesMOB_SCN-REQ_format( ) { Management Message Type=548— Scan duration8Units are frames Interleaving interval8Units are frames Scan iteration8In frames N_Recommended_BS8Number ofneighboringBSs to be scanned For (i=0; i<N_Recommended_BS;i++) {  Recommended BS_ID48BS Identifier }}
Referring to Table 1, the MOB_SCN-REQ message has a plurality of Information Elements (IEs). The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a desired scan duration during which pilot signals from the neighbor BSs are scanned, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings in the case of iterative scanning, and “Recommended BS_ID” identifying a desired BS to be scanned.
Upon receipt of the MOB_SCN-REQ message, the serving BS 230 replies to the MSS 210 with a Mobile Scanning Interval Allocation Response (MOB_SCN-RSP) message containing scanning information for the MSS 210 and a scan duration set to non-zero.
The MOB_SCN-RSP message has the following structure.
TABLE 2SizeSyntax(bits)NotesMOB_SCN-RSP_format( ) { Management Message Type=558— Scan duration8Units are frames. WhenScan duration is set to zero,no scanning parameters arespecified in the message.When MOB_SCN-RSP issent in response toMOB_SCN-REQ, settingScan duration to zerodenies MOB_SCN-REQ. Report mode20b00: no report0b01: periodic report0b10: event triggered report0b11: reserved; shall be setto zero reserved6Shall be set to zero Report period8Available when the value ofReport mode is set to 0b01.Report period in frames. Report metric8Bitmap indicating metricson which the correspondingtriggers are based:Bit 0: BS CINR meanBit 1: BS RSSI meanBit 2: Relative delayBit 3: BS RTDBit 4-7: reserved; shall beset to zero If (Scan duration!=0) { Start frame4— reserved4Shall be set to zero Interleaving interval8Duration in frames Scan iteration8— N_Recommended_BS8Number of neighboring BSsto be scanned for (i=0; i<N_Recommended_BS;i++) {  Recommended BS_ID48BS Identifier } }}
Referring to Table 2, the MOB_SCN-RSP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Scan duration” indicating a scan duration during which the MSS is to scan, “Report mode”, “Report period” used when the report mode is a periodic report, “Report metric” indicating the type of information to be reported as a scanning result, “Start frame” indicating the start of the scanning, “Scan iteration” indicating the number of iterative scannings in the case of periodic scanning, “Interleaving interval” indicating the time interval between scannings, and “Recommended BS_ID” identifying a desired BS to be scanned. If Scan duration is 0, it implies that the scanning request from the MSS is rejected. Information indicating the scanning result may be Carrier-to-Interference and Noise Ratio (CINR), Received Signal Strength Indicator (RSSI), relative delay, or Round Trip Delay (RTD).
Upon receipt of the MOB_SCN-RSP message containing the scanning information, the MSS 210 scans pilot channel signals from the serving BS 230 and the neighbor BSs in correspondence with the parameters included in the MOB_SCN-RSP message in step 217.
Meanwhile, the serving BS 230 discontinues data transmission to the MSS 210, buffering data for the MSS 210 during the scanning in the MSS 210 in step 219.
After the pilot scanning, the MSS 210 sends a Mobile Scanning Result Report (MOB_SCN-REP) message to the serving BS 230 to report the scanning result in step 221.
The MOB_SCN-REP message is configured in the following structure.
TABLE 3SizeSyntax(bits)NotesMOB_SCN-REP_format( ) { Management Message Type=608— Report mode10: Event triggered report1: Periodic report reserved7Shall be set to zero Report metric8Bitmap indicating presenceof certain metrics:Bit 0: BS CINR meanBit 1: BS RSSI meanBit 2: Relative delayBit 3: BS RTDBit 4-7: reserved; shall be setto zero N_BS8Number of BSs to bescanned for (i=0; i<N_BS; i++) {  BS_ID48BS Identifier  Scanning result8This field contains thescanning resultcorresponding to Reportmetric (CINR/RSSI/Relativedelay/RTD/etc. }}
Referring to Table 3, the MOB_SCN-REP message has a plurality of IEs. The IEs include “Management Message Type” identifying the type of the transmitted message, “Report mode” indicating a mode in which the MSS reports the scanning result, “Report metric” indicating the type of information reported as a scanning result, “BS_ID” identifying a scanned BS, and “Scanning result” indicating the scanning result for the BS. “Scanning result” is included in the MOB_SCN-REP message according to the presence or absence of information to be reported. The scanning result may be CINR, RSSI, relative delay, or RTD.
In the typical IEEE 802.16e communication system, since signaling transmission/reception is carried out between a fixed BS and an MSS via a direct link, as shown in FIG. 2, a highly reliable radio communication link can be easily established between them. Yet, due to the fixed position of the BS, a radio network cannot be configured with flexibility. As a result, it is difficult to provide an efficient communication service in a radio environment with a fluctuating traffic distribution or a significant change in the number of calls.
To overcome the above shortcoming, a multi-hop relay data transmission scheme can be implemented through fixed Relay Stations (RSs), mobile RSs or general MSSs in a typical cellular wireless communication system such as the IEEE 802.16e communication system. The multi-hop relay wireless communication system may adaptively reconfigure a network quickly according to a communication environment change and efficiently operate the entire wireless network. Such a multi-hop relay wireless communication system also extends a cell service area and increases system capacity. In the case of a bad channel status between a BS and an MSS, an RS is installed between them, thus establishing a multi-hop relay path through the RS, so a good radio channel can be provided to the MSS. Also, with the use of the multi-hop relay in a cell boundary area with a bad channel state, a high-speed data channel can be provided and the cell service area can be expanded.
FIG. 3 shows a multi-hop relay wireless communication system which includes a BS 310, a plurality of MSSs 311, 313, 331 and 333, and an RS 320 for providing a multi-hop relay path between the BS 310 and an MSS. Signals are transmitted and received among the BS 310, the RS 320, and the MSSs 311, 313, 331 and 333 in OFDM/OFDMA. The BS 310 manages a cell 300, and the MSSs 311 and 333 within the coverage area of the cell 300 and the RS 320 can communicate directly with the BS 310. Yet, the MSSs 331 and 333 in an area outside the cell 300 cannot communicate directly with the BS 310. Thus, the RS 320 covers the area 330 and relays signals between the BS 310 and the MSSs 331 and 333. In this way, the MSSs 331 and 333 can send/receive a signal to/from the BS 310 via the relay 320.
As described above, in the multi-hop relay wireless communication system using an RS, an MSS can communicate with a BS via the RS or by a direct link. Therefore, services and functions available in legacy wireless communication systems must also be provided in the multi-hop relay wireless communication system.
Since the communication of the MSS is expanded to the BS and the RS in a multi-hop relay BWA communication system, the MSS must scan neighbor RSs as well as neighbor BSs, for active communications. Legacy systems give no considerations to the multi-hop relay scheme and thus there is no specified scanning method involving an RS. Accordingly, there exists a need for defining a signal procedure for scanning in an MSS in the multi-hop relay BWA communication system.